1. Field of the Invention
This invention relates to an apparatus for pretreating particulate feed material for a rotary kiln with heated exit gases from the kiln, as is utilized, for example, to produce Portland cement. In particular, this invention relates to such preheaters that comprise an assembly of cyclone dust separators and an auxiliary furnace to additionally heat feed material after the feed material has been preheated but prior to the feed material entering the rotary kiln.
2. Description of the Prior Art
Preheaters for rotary kilns known to the prior art that involve preheating finely divided raw material suspended in and moving generally counter to the flow of heated kiln exit gases flowing through one or more cyclone dust separators are disclosed in such patents as Czechozlovakian Pat. No. 48,169 of 1934; published German Pat. application No. K 156,877 of 1940; U.S. Pat. Nos. 2,648,532 and 2,663,560 of 1953; many others of such patents are identified in U.S. Pat. No. 3,441,258 of 1969 and German Auslegeschrift 1,941,045 published in 1970.
Preheaters of the aforementioned type but which are additionally provided with an auxiliary furnace having one or more auxiliary burners to additionally heat feed material after the feed material has been preheated but prior to the feed material entering the rotary kiln are disclosed in patents such as U.S. Pat. Nos. 3,235,239 of 1966; 3,452,968 of 1969; 3,834,860 of 1974; 3,869,248; 3,873,331; 3,881,862; 3,891,382; 3,891,383; 3,914,098; 3,925,091 and 3,926,651, all of 1975; and 3,932,116 and 3,932,117 of 1976.